1. Field of the Invention
The invention relates to the field of lighter-than-air vehicles and, in particular, to an improved ballonets and a system for pressurizing same.
2. Description of Related Art
There are three general types of non-rigid vehicles: those comprising a single gas filled bag; several gasbags joined together in series; and, of course, those having a multiple number of gasbags within a non-rigid envelope. One of the major problems with non-rigid lighter-than-air vehicles is keeping the bag from bursting as the ambient pressure decreases with altitude or from collapsing when desending from altitude. The main method of preventing such events is to incorporate ballonets in the vehicle, which are inflatable gasbags within the Helium bag. The vehicle is designed to fly with partially inflated ballonets that can be inflated with air, causing the Helium volume to contract or, deflated, causing the Helium volume to expand. Thus, at altitude, the ballonets may be almost collapsed, providing the necessary "room" for the Helium to expand as ambient air pressure has decreased. As the vehicle desends into denser atmosphere, the ballonets are inflated to insure that the Helium gasbag does not collapse or even locally sag. Additionally, ballonents can play a roll in altitude control. An example of ballonets installed on a lighter-than-air vehicle can be found in U.S. Pat. No. 5,143,322, "Ground Handling, Altitude Control And Longitudinal Stability Of Airships" by E. W. Mason.
Prior art methods of pressurizing and filling the ballonets typically involved the use of ram air scoops. Examples of this type system can be found in U.S. Pat. No. 1,475,210, "Airship" by R. H. Upson and U.S. Pat. No. 2,331,404, "Airship" by H. R. Liebert. In the Liebert design, the ram air scoops are located behind the propellers and thus less dependent upon the speed of the airship. However, if the ship were at very low speeds filling, of course, would be proportionally slower. This would be true even with the Liebert design, because the speed of the airship is proportional to the rotational speed of the propeller.
In U.S. Pat. No. 1,580,004, "Airship" by A. Bradford and U.S. Pat. No. 1,797,502, "Airship by C. S. Hall separate pumps are used for pressurizing the ballonets. Additionally, the Hall design provide heaters to heat the pressurized air. Since the ballonet is located in the middle of the main Helium filled gasbag, heating of the Helium could also be accomplished. The problem with these designs is that the ballonets are located centrally and fill valves and lines are, necessarily, co-located. Thus they are difficult to reach for maintenance and repair or removal. Additionally, the need for such fill valves and lines add weight.
Thus, it is a primary object of the invention to provide a ballonet system for a lighter-than-air vehicle.
It is another primary object of the invention to provide a ballonet system for a lighter-than-air-vehicle that is independent from other systems of the vehicle.
It is a further object of the invention to provide a ballonet system for a lighter-than-air vehicle that allows the volume of air in each ballonet to be individually varied.
A still further object of the invention is to provide a ballonet system for a lighter-than-air vehicle that provides rapid filling and venting of the individual ballonets.